Don't hide V8 symbols in debug builds

gni/v8.gni

 # Copyright 2016 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/v8_target_cpu.gni")
 
 declare_args() {
   # Indicate if valgrind was fetched as a custom deps to make it available on
   # swarming.
   v8_has_valgrind = false
 
   # Indicate if gcmole was fetched as a hook to make it available on swarming.
   v8_gcmole = false
 
   # Turns on compiler optimizations in V8 in Debug build.
   v8_optimized_debug = true
 
+  # Support for backtrace_symbols on linux.
+  v8_enable_backtrace = ""
+
   # Enable the snapshot feature, for fast context creation.
   # http://v8project.blogspot.com/2015/09/custom-startup-snapshots.html
   v8_use_snapshot = true
 
   # Use external files for startup data blobs:
   # the JS builtins sources and the start snapshot.
   v8_use_external_startup_data = ""
 }
 
 if (v8_use_external_startup_data == "") {
   # If not specified as a gn arg, use external startup data by default if
   # a snapshot is used and if we're not on ios.
   v8_use_external_startup_data = v8_use_snapshot && !is_ios
 }
 
+if (v8_enable_backtrace == "") {
+  v8_enable_backtrace = is_debug && !v8_optimized_debug

[Michael Achenbach, 2016/07/20 11:55:30]

Consider turning it on by default for all debug builds if the increase in binary
size is not too much.

+}
+
 ###############################################################################
 # Templates
 #
 
 # Points to // in v8 stand-alone or to //v8/ in chromium. We need absolute
 # paths for all configs in templates as they are shared in different
 # subdirectories.
 v8_path_prefix = get_path_info("../", "abspath")
 
 # Common configs to remove or add in all v8 targets.
@@ skipping 12 matching lines @@
 
   # TODO(crbug.com/621335) Rework this so that we don't have the confusion
   # between "optimize_speed" and "optimize_max".
   if (is_posix && !is_android && !is_nacl && !using_sanitizer) {
     v8_add_configs += [ "//build/config/compiler:optimize_speed" ]
   } else {
     v8_add_configs += [ "//build/config/compiler:optimize_max" ]
   }
 }
 
+if (is_posix && v8_enable_backtrace) {
+  v8_remove_configs += [ "//build/config/gcc:symbol_visibility_hidden" ]
+  v8_add_configs += [ "//build/config/gcc:symbol_visibility_default" ]
+}
+
 # All templates should be kept in sync.
 template("v8_source_set") {
   source_set(target_name) {
     forward_variables_from(invoker, "*", [ "configs" ])
     configs += invoker.configs
     configs -= v8_remove_configs
     configs += v8_add_configs
   }
 }
 
@@ skipping 11 matching lines @@
 }
 
 template("v8_component") {
   component(target_name) {
     forward_variables_from(invoker, "*", [ "configs" ])
     configs += invoker.configs
     configs -= v8_remove_configs
     configs += v8_add_configs
   }
 }